Hydro transformer

ABSTRACT

A hydraulic transformer includes a multiplicity of displacers each guided in a displacer chamber. Pressure medium supply and discharge to and from the displacer chambers is controlled through the intermediary of control means provided with control recesses. The effective position of the control recesses in relation to the dead center positions of the displacers is variable, with each displacer volume being adapted to be connected with a dead space in a commutation phase upon transition between two adjacent control recesses.

The invention relates to a hydraulic transformer in accordance with thepreamble of claim 1.

A hydraulic transformer is a unit wherein an energy flow Q₁×p₁ istransformed into an energy flow Q₂×p₂ through hydraulic coupling of ahydrostatic motor and a pump. In the process, only the amount ofhydraulic energy required for driving a consumer that is connected tothe pump is withdrawn from an existing pressure supply. Such hydraulictransformers may be designed as radial piston engines, axial pistonengines, or in accordance with other kinematic function principles,e.g., as vane-cell machines.

U.S. Pat. No. 3,188,963 discloses a hydraulic transformer having theform of a swashplate motor, wherein displacers guided in a rotatablecylinder are supported on a stationary swash plate. The angle of theswash plate determines the piston stroke of the displacers. Pressuremedium supply and discharge are performed with the aid of a control dischaving four control kidneys, wherein the respective pairs of controlkidneys are associated with the motor and the pump.

In U.S. Pat. No. 3,079,864 a hydraulic transformer in vane-cellconstruction is disclosed. In this solution, a multiplicity ofdisplacers translatable in a radial direction are mounted in a rotor andbiased against a cam ring. Pressure medium supply and discharge areperformed, similar to the above described solution, with the aid of acontrol disc arranged on the front end side.

From WO 97/31185 A1 and from the reference, “Ein neuer alterBekannter—der Hydrotransformator” [A new old acquaintance: the hydraulictransformer], Siegfried Rotthäuser, Peter Achten; O+P “Öhydraulik andPneumatik” 42 (1998) No. 6; p. 374 et seq., the so-called INNAShydraulic transformer is known, wherein the transformation ratio, i.e.the ratio between the supply pressure and the pressure for supplying theconsumer, is variable. To this end, a control disc is provided withthree control kidneys, the relative position of which to the dead centerpositions of the displacers is variable by rotation relative to theswash plate of an axial piston machine.

From DE 100 252 48.6, a further development of the hydraulic transformerdisclosed in WO 97/31185 A1 is known. In this solution, the pressuremedium ports (supply port, work port, tank port) open in a radialdirection into the rotatable control means, so that the forces acting inan axial direction are reduced.

In hydraulic transformers of this design, the displacer chambers areinherently also shifted outside of the dead center positions, whereinthis shifting may take place at arbitrary piston velocities. Shiftingtakes place within a substantially smaller rotational angle interval incomparison with pumps and motors, so that comparatively high pressuregradients may occur, which may lead to excessively high mechanicalstrains on the hydraulic transformer and high noise emission.

Besides these high pressure gradients, particularly pressure adaptationduring shifting is very difficult to implement in practice. In the idealcase, the pressure should rise or drop linearly to the subsequentpressure level during the entire rotational angle interval. It wasfound, however, that such a shifting property cannot be realized acrossthe entire operating range of the transformer. The rigid commutationgeometry may lead to cavitations and pressure peaks in the commutationranges, so that the above described noise emissions and the mechanicalstrain on the hydraulic transformer are increased further.

Before this background, the invention is based on the object ofproviding a hydraulic transformer wherein the load is reduced bypressure gradients in the commutation range.

This object is achieved through a hydraulic transformer having thefeatures of claim 1.

In accordance with the invention, the hydraulic transformer is providedwith a multiplicity of displacers each guided in a displacer chamber andcapable of being connected through commutation means including apressure port, a consumer port, or a tank port, the relative position ofthe commutation means being variable relative to the dead centerpositions of the displacers. In accordance with the invention, the oilvolume of the displacer chamber to be shifted is increased during thecommutation phase. This is achieved in particular in that in thiscommutation phase, the respective displacer volume is connected with acommutation chamber. As a result of these increases in the oil volume,the pressure gradients, pressure peaks, and noise emissions are reducedconsiderably in the commutation phase.

In a particularly preferred embodiment, the control means include threecontrol recesses distributed at the periphery, with the commutationchambers opening into respective ranges between two adjacent controlrecesses.

Here it is particularly preferred if these control recesses have anapproximate kidney shape, and the commutation chambers each open intoone of the kidney separation webs.

In a preferred embodiment, the control kidneys and through bores of thecommutation chambers are formed in a control disc of the control means.

In a preferred manner, the commutation means have next to the controldisc a base body in which a part of the commutation chamber is formednext to the through bores of the control disc.

It is particularly advantageous if the volume of each commutationchamber is greater or at least equal to the displacement volume of adisplacer.

The volume of the commutation chamber should, however, preferably beless than five times the displacement volume. This range may, however,vary in accordance with system pressure, switching frequency, andgeometry of the control bores.

The hydraulic transformer of the invention preferably has the form of anaxial piston bent-axis unit. As was already mentioned at the outset, theinvention may also be applied in other kinematic functional principlesfor hydraulic transformers.

Further advantageous developments of the invention are subject mattersof the remaining subclaims.

In the following, a preferred practical example of the invention shallbe explained in more detail by referring to schematic drawings, wherein:

FIG. 1 is a three-dimensional representation of a hydraulic transformerin bent-axis design;

FIG. 2 is a front view of a control member of the hydraulic transformerof FIG. 1;

FIG. 3 is a three-dimensional representation of the control member ofFIG. 2; and

FIG. 4 is a longitudinal sectional view of the control member of FIGS. 2and 3.

FIG. 1 shows a three-dimensional schematic representation of a hydraulictransformer 1 executed in bent-axis design. In principle, a likehydraulic transformer 1 may be represented as a combination of ahydrostatic motor and a hydraulic pump mechanically coupled to eachother. In accordance with the prior art described at the outset,hydraulic transformers may be realized through variable displacer units,with axial piston machines or vane cell machines preferably being used.Fundamentally it is, however, possible to employ any displacer unitwhere the displacers may be controlled such that they may successivelybe taken into operative connection with three pressure levels: thesupply pressure, the tank pressure, and the consumer pressure (workpressure).

The hydraulic transformer 1 in accordance with FIG. 1 includes an angledhousing 2 in which displacers guided inside a cylinder drum, a driveflange, and a drive shaft are arranged. To the angled housing 2 acontrol housing 4 is attached which is closed by a cap 5. Supply anddischarge of the pressure medium to and from the cylinder chambers iseffected through a control member 12 accommodated in the control housing4 which may be adjusted to vary the transmission ratio between pump andmotor. The commutation means may be adjusted in relation to the deadcenter positions of the displacers with the aid of adjusting means, suchas with the aid of an electric motor 6 or any other suitable drivemechanism, e.g., a gear drive.

On the angled housing 2 and on the cap 5 a work port B, a tank port T,and a supply port A are provided. These ports may be executed as axialor radial ports.

The construction of the bent-axis unit including the displacers issufficiently known from the prior art. In this regard, reference ismade, e.g., to patent application DE 100 252 48, so that a detaileddescription of the bent-axis unit may be omitted.

The control member 12 of FIGS. 2 to 4 is rotatably mounted in thecontrol housing 4 and includes at its outer periphery a flange 14 foraxial contact with a gear (not shown). By means of this gear it ispossible to adjust the control member 12 in relation to the dead centerpositions of the displacers. The control member 12 hat on its end-faceside (view of FIG. 2) a control disc 16 which sealingly contacts thecylinder drum rotatably mounted in the angled housing 2. Inside thiscylinder drum, the displacers are guided which are translatable in anaxial direction and supported on a bent axis. Three control kidneys 18,20, 22 distributed on the periphery extend through the control disc 16.Between two respective adjacent control kidneys there remains a kidneyseparation web 25 into which an axial blind bore 23, 27 or 29 opens.

As is particularly evident from the three-dimensional representation ofthe control member 12 in FIG. 3, the control disc 16 is part of a basebody 24, at the outer periphery of which the flange 14 is formed. In thebase body 24, connection passages 26, 28, 30 are formed whereby thecontrol kidneys 18, 20 and 22, respectively, are connected with theassociated pressure medium ports. In the represented practical example,the control kidney 18 is connected via the connection passage 26 andradially merging passages 32 with the tank port T, control kidney 20 isconnected via the connection passage 28 and an oblique passage 36extending obliquely to the axis 34 of the control member 12 with theconsumer or work port B, and control kidney 22 is connected via threebores 38 extending in parallel with the axis with the supply port A.I.e., depending on their position relative to the control kidneys 18,20, 22, the displacers may be subjected to the pressure at the tank portT, at the work port B, or at the supply port A. The width of the kidneyseparation webs 25 is selected such that a displacer volume may becovered by the kidney separation web 25 in the commutation phase betweentwo adjacent control kidneys. In conventional solutions, these kidneyseparation webs are closed, so that in the commutation phase a completecoverage of the displacer chamber ensues. In accordance with theinvention, in the commutation phase the displacer chambers located inthe range of the kidney separation webs 25 are connected with deadspaces 40, 42 and 44 represented in FIG. 3 via the blind bores 23, 27and 29. These have the form of axial and radial or oblique bore sectionsin the base body 24 and are represented externally of the control member12 in FIG. 3 for the sake of clarity. The geometries of the abovedescribed connection passages 26, 28, 30 and of dead spaces 40, 42, 44separated therefrom depend on the geometry of the base body 24. In therepresented practical example, the dead space 44 is essentially formedby a centrally arranged, axially extending cavity that is connected withthe blind bore 29 through a transverse bore. The two commutationchambers 40 and 42 are formed by radially offset bore sectionssubstantially extending in the axial direction and interconnected byrespective oblique or radial bores. The dead space 44 is closed againstthe control disc 16 by a screw plug 45. The axially extending bores ofthe two other dead spaces are introduced into the end face side of thecontrol member 12 facing away from the control disc 16 and are closed byscrew plugs 46. Likewise, the radial bores of the dead spaces are closedexternally by screw plug. The volume of the commutation chambers, whichalso encompasses the volume of the blind bores 23, 27, 29, in each casecorresponds to at least the displacement volume of one displacer andshould not exceed five times the displacement volume of one displacer inorder to minimize compression/decompression losses.

The displacers accommodated in the rotating cylinder drum are in thecourse of their rotary movement successively connected with the threecontrol kidneys 18, 20 and 22 and subjected to the correspondingpressure. In the commutation phase the respective displacer volume isconnected through one of the three through bores 23, 27 and 29 with theassociated dead space 40, 42 or 44, respectively, so that in practice,the oil volume of the associated displacer chamber is increased by thevolume of the dead space. Owing to the resulting smooth shiftitng, theabove described strains and noise emissions are reduced considerably,and thus the effectivity of the hydraulic transformer is improved incomparison with conventional solutions. First test runs with thehydraulic transformer of the invention confirm its superiority over theknown solutions.

As was already mentioned, the shape of the cavities inside the base body24 is of minor importance. What is essential is that the volumes of thedead spaces effective in the commutation zones are dimensioned inaccordance with system pressure, switching frequency and geometry of thethrough bores, such that the rigidity of the “oil spring” is reduced inthe commutation phase.

A hydraulic transformer includes a multiplicity of displacers eachguided in a displacer chamber. Pressure medium supply and discharge toand from the displacer chambers is controlled through the intermediaryof control means provided with control recesses. The effective positionof the control recesses in relation to the dead center positions of thedisplacers is variable, with each displacer volume being adapted to beconnected with a dead space in a commutation phase upon transitionbetween two adjacent control recesses.

List of Reference Symbols

-   -   1 hydraulic transformer    -   2 angled housing    -   4 commutation means    -   6 handle    -   10 control housing    -   12 control member    -   14 flange    -   16 control disc    -   18 control kidneys    -   20 control kidneys    -   22 control kidneys    -   23 through bore    -   24 base body    -   25 kidney separation web    -   26 connection passage    -   27 through bore    -   28 connection passage    -   29 through bore    -   30 connection passage    -   32 passages    -   34 axis    -   36 oblique passage    -   38 bores    -   40 commutation chamber    -   42 commutation chamber    -   44 commutation chamber    -   45 screw plug    -   46 screw plug

1. A hydraulic transformer, comprising a multiplicity of displacersguided in a displacer volume, and commutation means for shiftingpressure medium supply and discharge to and from the displacers, whereinsaid commutation means include at least two control recesses connectedwith a pressure port, consumer port, or tank port, the relativepositions of which are variable in relation to the dead-center positionsof said displacers, characterized by a dead space through theintermediary of which the displacer volume is increased in a commutationphase.
 2. The hydraulic transformer in accordance with claim 1, whereinsaid control means include three control recesses (18, 20, 22)distributed on the periphery, and said dead spaces open into respectiveranges between said control recesses.
 3. The hydraulic transformer inaccordance with claim 2, wherein said control recesses are controlkidneys, and said dead spaces open into respective kidney separation webbetween two adjacent control kidneys.
 4. The hydraulic transformer inaccordance with claim 2, wherein said control means include a controldisc in which said control kidneys and through bores of said dead spacesare formed.
 5. The hydraulic transformer in accordance with claim 4,wherein a part of said dead spaces next to said through bores is formedin a base body of said commutation means, in which base body connectionpassages leading to said ports are provided at least in portions.
 6. Thehydraulic transformer in accordance with claim 1, wherein the volume ofeach dead space is larger than or equal to the displacement volume of adisplacer.
 7. The hydraulic transformer in accordance with claim 6,wherein the volume of said dead space is less than five times thedisplacement volume.
 8. The hydraulic transformer in accordance withclaim 1, wherein one of said dead spaces is formed to be substantiallyaxial, and said two other dead spaces are formed to be substantiallyoffset with respect to the axis of said control member.
 9. The hydraulictransformer in accordance with claim 1, wherein said displacers arepistons of an axial piston bent-axis unit.